1. Field of the Invention
This invention relates generally to a magnetoresistive sensor, and more particularly to such a sensor based on extraordinary magnetoresistance (EMR).
2. Description of the Related Art
A magnetoresistive sensor based on extraordinary magnetoresistance (EMR) has been proposed as a read-head sensor for magnetic recording hard disk drives. Because the active region in the EMR sensor is formed of nonmagnetic semiconductor materials, the EMR sensor does not suffer from the problem of magnetic noise that exists in read-head sensors based on giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR), both of which use magnetic films in their active regions.
The EMR sensor includes a pair of voltage leads and a pair of current leads in contact with one side of the active region and an electrically conductive shunt in contact with the other side of the active region. In the absence of an applied magnetic field, sense current through the current leads passes into the semiconductor active region and is shunted through the shunt. When an applied magnetic field is present, current is deflected from the shunt and passes a longer distance through the semiconductor active region, thereby increasing the resistance of the device because of the higher resistivity of the semiconductor active region. The change in electrical resistance due to the applied magnetic field is detected across the voltage leads. EMR is described by T. Zhou et al., “Extraordinary magnetoresistance in externally shunted van der Pauw plates”, Appl. Phys. Lett., Vol. 78, No. 5, 29 Jan. 2001, pp. 667–669. An EMR sensor for read-head applications is described by S. A. Solin et al., “Nonmagnetic semiconductors as read-head sensors for ultra-high-density magnetic recording”, Appl. Phys. Lett., Vol. 80, No. 21, 27 May 2002, pp. 4012–4014.
One of the problems of the EMR sensor is that its magnetoresistance is an approximately quadratic function of the applied magnetic field. Thus the magnetoresistance response is small and nonlinear in the presence of the small magnetic fields from the recorded magnetic media. Biasing of the EMR sensor has been proposed by an asymmetric location of the voltage leads.
Biasing of the EMR sensor has also been proposed by use of a biasing magnet located on a substrate with a spacer layer on top of the magnet and the EMR sensor formed on top of the spacer layer. This structure is described in U.S. Pat. No. 6,714,374 and proposes a layer of a CoCr-based alloy with perpendicular magnetization for the biasing magnet. This structure is relatively difficult to fabricate because the sensor's semiconductor layers must be formed on top of the CoCr metal layer. In addition, the use of a fixed composition for the CoCr-based alloy makes it difficult to adjust the magnetization and coercivity of the biasing magnet, which may be required during fabrication of the sensor.
Co-pending application Ser. No. 10/883,204 filed Jun. 30, 2004, titled “EXTRAORDINARY MAGNETORESISTANCE SENSOR WITH PERPENDICULAR MAGNETIC BIASING BY AN ANTIFERROMAGNETIC/FERROMAGNETIC EXCHANGE-COUPLED STRUCTURE”, and owned by the same assignee as this application, describes biasing of an EMR sensor using a ferromagnetic layer with perpendicular exchange-coupling to an antiferromagnetic layer.
What is needed is an EMR sensor with an improved perpendicular magnetic biasing layer that is easier to fabricate and that does not use an antiferromagnetic layer.